Cerebrospinal fluid (CSF) is a clear bodily fluid that is primarily produced by the choroid plexus and continuously circulates throughout the ventricular system of the brain and around the spinal cord. The essential function of CSF is to provide a protective cushion to the brain and spinal cord in that it acts as a shock absorber by keeping the brain and spinal cord buoyant, which ultimately can prevent injuries to the central nervous system.
The abnormal accumulation of CSF in the brain ventricles consequently leads to the condition of hydrocephalus through the obstruction or excessive production of CSF in the brain. Hydrocephalus, as a result, is characterized by an elevated intracranial pressure (ICP) which ultimately causes pressure that can compress the brain tissue and dilate the ventricles. If left untreated, hydrocephalus can lead to other dangerous conditions, including subdural hematoma, impaired blood flow, coma, or even the eventual death of a patient. Thus, to effectively reduce elevated ICP, the drainage and rerouting of CSF to a secondary location within the body is an essential solution for patients with congenital or acquired hydrocephalus.
The removal and drainage of CSF has been achieved with varying levels of success in the past and present through the use of shunt systems. Shunt systems are typically made up of a ventricular catheter, which is inserted into the brain ventricle and connected to a valve that conducts the fluid away from the brain to be reintroduced into the peritoneal cavity or into the vascular system through a distal catheter to essentially maintain the proper pressure in the brain ventricles. Although many of the existing shunt systems have been implemented with successful results, they can still present problems given certain circumstances.
A primary example of an essential problem that has existed within the use of typical shunt systems is in the inability to adjust the threshold pressure within the shunt valve. Shunt systems typically allow fluid flow only when the fluid pressure reaches a threshold pressure for the shunt valve. However, due to the constantly changing physiological parameters of a patient over time, the threshold pressure must be adjusted. For example, an initial setting on the valve can be determined based upon the patient's preoperative ventricular CSF pressure, which could be most optimal at a relatively low threshold pressure. Once the shunt system has been implanted, the pressure may often need further adjustment to stabilize the ventricle size. This is essential because if the valve pressure is not adjusted, it could lead to the overdrainage of CSF from the brain ventricle or the accumulation of CSF within the ventricles resulting in an elevated ICP. As an alternative to surgically re-implanting the shunt system for adjustments after the initial threshold pressure has been defined, non-invasive methods have been in use to effectively achieve this.
The use of a programmable shunt system, which was first disclosed by Hakim in U.S. Pat. Nos. 4,615,691 and 4,772,257, has most significantly provided an efficient method for overcoming the difficulties discussed regarding the constant need for pressure adjustment of the shunt valve. The methods disclosed in these patents for an adjustable-pressure valve is commercially known as the Codman Hakim Programmable and Medtronic Strata valves. These particular shunts use an externally adjustable CSF shunt valve which has a variable pressure through the implementation of a magnetic field which is applied outside of the patient's body. The magnetic field ultimately actuates an internal stepper motor to vary the threshold pressure within the shunt valve. Although this has provided an important solution to some of the most essential problems associated with shunts, existing shunt systems in general still do not have the ability to adjust threshold pressures autonomously in accordance with the constantly changing physiological constraints of a patient which inevitably change over time.
The concept of using a sensor for detecting pressure changes which can provide an externally communicated signal along with a direct signal to the actuating element for autonomous valve pressure adjustment, is, however, a method for improving upon certain difficulties concerning fluid flow and pressure which has also been addressed in a number of different patents. These patents all discuss a variety of different methods, but there are also many limitations to the methods presented due to how the sensor and actuating elements effectively adjust the threshold pressure.
These limitations are often a result of the particular means for actuation, such as the constant reliability to an electromagnetic actuator. This particular form of actuation in itself has its own restrictions, especially with regard to how it can be used or coupled to a sensing element and how that sensing element directly functions with the actuating element with regard to shunt systems in general. By using a different kind of actuator then magnetic energy, i.e., one that can act as both an actuator and as a transducer through taking advantage of the deflection used to detect the pressure imposed upon it, a reduction in the number of mechanical components can also be an advantageous result in that it would provide a simplified assembly and fabrication method for the mechanical features of the shunt valve. The implementation of existing magnetically actuated shunt valves also do not provide a means for a sensing element that is directly coupled to the means for actuation, which can also be improved upon through the use of alternative actuation methods.
Accordingly, an implantable shunt system which is capable of adjusting its threshold valve pressure through the use of alternative methods for an actuator and the mechanical properties by which that actuator functions with, along with an alternative means for sensing, can provide a number of advantages over previously existing shunt systems. The problems that can be improved upon concern not only the ability to have an automatically adjustable pressure valve, which is also externally programmable, but also including the detection of pressures that exist within the implanted shunt assembly which can be communicated to an external point outside of the patient's body.